The structure of a double layer capacitor is well-known to those skilled in the art. Such a cell comprises a pair of electronically conductive elements, for example, metal foil or discs, having an electrolyte solution sandwiched therebetween. The electrolyte solution is divided into two electrodes by an ion-permeable separator. The electrolyte solution is a liquid or paste which is sealed within the capacitor structure using, for example, a gasket. A capacitor of this type is described in, for example, U.S. Pat. No. 3,536,963.
It is also known to arrange a plurality of carbon-containing, bipolar electrode structures in functional arrangement, and to provide an electrolyte liquid or paste between adjacent pairs of bipolar electrodes. Such a multicell device is shown in U.S. Pat. No. 4,164,068. This patent discloses a structure consisting of a plurality of bipolar, carbon-plastic electrode structures. The structures are formed by first molding an electronically conductive, carbon-containing, plastic sheet, and then providing a dielectric frame around each of the resulting sheets. When the individual elements are welded together, chambers are formed which are capable of holding liquid or paste electrolyte between each adjacent pair of bipolar electrodes. These chambers are filled with a suitable liquid or paste electrolyte composition.
The invention avoids the problems associated with electrochemical devices or double-layer capacitors of the aforesaid type which contain liquid or paste electrolyte material. Devices which utilize a liquid or paste electrolyte inevitably suffer from problems of leakage and the resulting hazards. Additionally, a non-liquid device would avoid the separate step of adding a seal or gasket to contain the electrolyte.
In Europe, considerable attention has been focused upon the fabrication of solid state batteries, based upon, for example, lithium metal. Lithium has been of interest due to its low density and highly electropositive nature. Such cells incorporate, for example, a lithium or lithium based anode, and a cathode containing a vanadium oxide compound, V.sub.6 O.sub.13, for example, as the active material. The lithium anode may be a metal foil. The electrolyte layer consists of a polymer such as polyethylene oxide and a lithium salt. The cathode structure consists of a composite material containing the active cathode material V.sub.6 O.sub.13, a polymer electrolyte material, and carbon in the form of acetylene black. These batteries have been found to be beneficial in terms of ease of construction, ruggedness, interfacial properties, open circuit voltage, energy density, and rechargability.
It is known and common to fabricate capacitors using ceramic materials. The use of ceramics in a solid state capacitor, however, involves serious drawbacks. First, the ceramic only operates at extremely high temperatures. Also, the ceramic material cannot be mixed effectively with another material to provide a composite material having a large operable surface area.
Apart from the aforesaid, electrochemical devices and double-layer capacitors of the type described which are known and in use today employ a liquid, paste, or molten electrolyte. The need exists for a device which does not suffer from the drawbacks of a device utilizing liquid or paste electrolyte, yet which has increased electrical characteristics due to large surface area and which is operable at moderate temperatures.